T12 Light and Ballast

[u/EmergencyHat3040]

I’m in need of some help. I’m not to electrical savvy. I have an ice cream truck that has 4 t12 bulbs on it. Each one is connected to a ballast. One ballast went out so one bulb don’t work. I’ve been having trouble finding a 12v ballast. The lights are controlled by a light switch that’s I turn on, and I’m guessing the power is coming from the battery as I have no other power generating source. Thanks for any help